1. Field of the Invention
The present invention relates generally to a method of manufacturing a semiconductor integrated circuit device that uses an SOI (silicon on insulator) type semiconductor substrate and, more particularly, to an effective technique with which a diode type photosensor and its signal processing circuit are mounted on one chip.
2. Description of the Related Art
A conventional semiconductor integrated circuit device using an SOI substrate is shown in a sectional view in FIG. 4. In the conventional device, a diode type photosensor 105 is of a so-called xe2x80x9cplanar type,xe2x80x9d and the diode type photosensor 105 and a portion of the associated signal processing circuit 103 are formed in a surface semiconductor that is insulated and isolated from the semiconductor substrate. A peripheral transistor 109 may be formed adjacent the photosensor 105 for current-voltage conversion. The signal processing circuit 103 is formed on the SOI substrate to obtain low voltage operation, low power consumption and higher operation speed, and to avoid the influence of noise.
In recent years, higher resolution is required for line type image sensor ICs and area image sensor ICs equipped with a diode type photosensor, and there has been a demand for downsizing of the cell on the part of the diode type photosensor. However, to reduce the size of the cell while keeping the S/N ratio of the photosensor at or above a given value is difficult to achieve. This is because the noise level is not decreased in proportion to the cell size, although the absolute value of a signal per unit cell becomes small to accompany the reduction of the cell size.
The present invention has been made to solve the problem above, and an object of the present invention is therefore to provide a method of manufacturing a diode type photosensor that has an adequate S/N ratio with a reduced cell size.
In order to attain the above object, the present invention takes the following measures:
(1) A method of manufacturing a semiconductor integrated circuit device using an SOI semiconductor substrate, the main surface thereof for forming a device being insulated and isolated by a buried insulating layer formed in the semiconductor substrate, the method being characterized by comprising the steps of:
forming the buried insulating layer in a part of the main surface of the substrate; and
forming a diode type photosensor in a region of the main surface of the substrate where the buried insulating layer is not formed.
(2) A method of manufacturing a semiconductor integrated circuit device using an SOI semiconductor substrate, the main surface thereof for forming a device being insulated and isolated by a buried insulating layer formed in the semiconductor substrate, the method being characterized by comprising the steps of:
partially removing from the semiconductor substrate with the buried insulating film formed across its entire main surface, the semiconductor substrate main surface and buried insulating layer; and
forming a diode type photosensor in the main surface of the substrate in a region where the removal has been performed.
(3) A method of manufacturing a semiconductor integrated circuit device, characterized in that the manufacturing method of the diode type photosensor comprises the steps of:
forming a trench in the semiconductor substrate; and
forming a diffusion layer on the side walls and the bottom of the trench.
(4) A method of manufacturing a semiconductor integrated circuit device, characterized in that the manufacturing method of the diode type photosensor further comprises the step of filling up with an insulating film the inside of the trench formed in the semiconductor substrate.
(5) A method of manufacturing a semiconductor integrated circuit device, characterized in that the manufacturing method of the diode type photosensor further comprises the step of filling up with polycrystalline silicon the inside of the trench formed in the semiconductor substrate.